1. Field of the Invention
This invention relates generally to the field of safety or “threat resistant” laminated glass products and polymeric interlayers used therein. This invention specifically relates to a polymeric sheet comprising specific mixed ion ionomers or ionomer blends, especially useful in high-strength laminates.
2. Description of Related Art
Glass laminated products have contributed to society for almost a century. Beyond the well known, every day automotive safety glass used in windshields, laminated glass is used in all forms of the transportation industry. It is utilized as windows for trains, airplanes, ships, and nearly every other mode of transportation. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric film or sheet, which is placed between the two glass sheets. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets of polycarbonate materials. Safety glass has further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric films or sheets.
The interlayer is typically made with a relatively thick polymer film or sheet, which exhibits toughness and bondability to provide adhesion to the glass in the event of a crack or crash. Over the years, a wide variety of polymeric interlayers have been developed to produce laminated products. In general, these polymeric interlayers must possess a combination of characteristics including very high optical clarity (low haze), high impact resistance, high penetration resistance, excellent ultraviolet light resistance, good long term thermal stability, excellent adhesion to glass and other rigid polymeric sheets, low ultraviolet light transmittance, low moisture absorption, high moisture resistance, excellent long term weatherability, among other requirements. Widely used interlayer materials include complex multi-component compositions comprising polymers such as polyvinylbutyral (PVB), polyurethane (PU), polyvinylchloride (PVC), metallocene-catalyzed linear low density polyethylenes, ethylene vinyl acetate (EVAc), ethylene acid copolymer ionomers, polymeric fatty acid polyamides, polyester resins such as poly(ethylene terephthalate), silicone elastomers, epoxy resins and elastomeric polycarbonates.
A more recent trend has been the use of glass laminated products in the construction business for homes and office structures. The use of architectural glass has expanded rapidly over the years as designers incorporated more glass surfaces into buildings. “Threat resistance” has become an ever increasing requirement for architectural glass laminated products. These newer products are designed to resist both natural and man made disasters. Examples of these needs include the recent developments of hurricane resistant glass, now mandated in hurricane susceptible areas, theft resistant glazings, and the more recent blast resistant glass laminated products designed to protect buildings and their occupants. These products have great enough strength to resist intrusion even after the frangible portion of the glass laminate has been broken, for example, by high force winds, by impact of flying debris or by a criminal attempting to break into a vehicle or structure.
In addition, glass laminated products have now reached the strength requirements for being incorporated as structural elements within buildings. An example of this would be glass staircases now being featured in many buildings.
A part of this trend has been the use of copolyethylene ionomer resins as the glass laminate interlayer material. Such ionomer resins offer significantly higher strength then found for the other common interlayer materials, such as polyvinyl butyral and ethylene vinyl acetate materials. For example, Friedman, et. al., in U.S. Pat. No. 6,432,522, disclose that polyvinyl butyral resins have a modulus (ASTM Method D638) of less than 5000 psi (34.5 MPa), and ethylene vinyl acetate materials have a modulus of 750-900 psi (5.2-6.2 MPa), while the copolyethylene ionomer resins have a modulus in the range of 34,000-80,000 psi (235-552 MPa).
The use of certain mixed metal ion-neutralized ionomeric material within glass laminates has been disclosed within the art. For example, Bolton, et. al., in U.S. Pat. No. 4,663,228 and U.S. Pat. No. 4,668,574, disclose a transparent laminated article which includes a water insoluble ionomer resin film comprising the metal salt of an ionomer resin prepared from ethylene and methacrylic acid monomers and, optionally, further partially neutralized by an organic diamine or triamine. They specify that a mixture of sodium and zinc ionomer resins may be used, and that both zinc and sodium ions may be used to neutralize the ionomer.
Smith, et. al., in U.S. Pat. No. 5,763,062, disclose a transparent article comprising an extruded ionomer resin film or sheet having a carboxylic acid content of between about 17 and 40 weight percent, the ionomer resin being essentially free of amines and having a thickness of at least about 0.5 mm. They disclose that “[s]uitable metal cations for neutralization are monovalent cations such as lithium, sodium, and potassium. Divalent cations such as magnesium, calcium, and zinc may also be used, alone or in combination with the monovalent cations, but often the metal carbonate or oxide is present as a haze producing impurity.” (U.S. Pat. No. 5,763,062, Column 6, line 1). They exemplify laminates which include sodium and sodium and lithium mixtures of metal neutralization agents.
Hanoka, in U.S. Pat. No. 6,114,046, and Hanoka, et. al., in U.S. Pat. No. 6,187,448 and U.S. Pat. No. 6,353,042, disclose photovoltaic solar cell modules and glass laminates which includes a layer of metallocene polyethylene disposed between two layers of a certain ionomers as an encapsulant material. Preferred ionomers include partially neutralized ethylene-methacrylic acid copolymers or ethylene-acrylic acid copolymers. They disclose that “the backskin layer 28 can be a thermoplastic polyolefin comprising a mixture of at least two acid copolymers such as a sodium acid copolymer and a zinc acid copolymer” (U.S. Pat. No. 6,187,448, column 6, lines 52-53). However, they further disclose that “The ionomer layers are thin (i.e., the order of 0.001-0.004 [inch] thick)” (U.S. Pat. No. 6,114,046, Column 2, line 66) and “The acid copolymer layers 14, 16, can have a thickness in the range of 0.001-0.004 inch” (1-4 mils) (U.S. Pat. No. 6,187,448, column 6, line 19). Hanoka, in U.S. Pat. No. 6,320,116, discloses solar cell modules which may include ionomer encapsulants which have been exposed to electron beam radiation. He discloses that “One example of a mixture of polyolefins is a mixture of Zn and Na ionomers along with a mineral filler.” (U.S. Pat. No. 6,320,116, column 6, line 8).
The high strength laminates of the present invention overcome the shortcomings disclosed within the art and provide durable glass laminates which additionally provide synergistically improved glass adhesion.